Today’s utility is a way to send and receive text messages through an alternate phone number. Text+ is a program that gives you that flexibility. Set up an account, then import your contacts. You can also set up a phone number (get a more localized number for an extra price).
With this program, you have the added advantage of texting over Wifi. Therefore, if you are on a plane flight (like I was the other day), I could pull out my iPad, connect up to the in-flight WiFi, and text away.
There are other in-app options so you can stay in contact with people.